New processes have been developed for the processing of lightly salted products from farmed cod in a project funded by AVS (R 11 006-010).
Farmed fish are usually processed before death, but this has caused certain problems with salt uptake and weight changes in products. It has now been shown that a salt uptake comparable to that in wild fish processed after death hardening can be achieved by controlling the composition of the brine and the salting methods.
There is a difference in the processing of farmed cod and wild cod, which lies in the fact that farmed cod is processed before death. The reason is that there is a greater risk of release if farmed cod is processed after death. In addition, the control of raw material procurement is easier than in traditional wild fish ice fishing, as various external factors, such as distance to the center, make it impossible to process wild fish before death. This difference in processing timing has meant that it has not been possible to transfer the processes used for wild fish to farmed fish as its processing properties differ from wild fish.
The main products from cod farming are fresh neck pieces that are transported to mainland Europe, but some of the products are also frozen. The advantage of selling aquaculture products is greater security of supply, as the control of raw material procurement is easier, raw material is fresher as it can be processed immediately after slaughter and the shelf life of products is longer. The chemical composition of farmed cod is similar to that of wild cod, but their physical characteristics are different. This means that changes in the muscle during processing, storage and cooking are different, such as there is a risk that farmed cod will be tougher and drier when boiled than wild fish.
The market for lightly salted products is desirable and is well suited for farmed cod, which is often whiter and thicker than wild cod. In Spain, a market has been built for lightly salted frozen cod products alongside traditional salted fish products. Lightly salted fish is often whiter and the symptoms of action are much milder than in salted fish.
The timing of processing of firefish has caused problems with salting, as salt uptake and weight gain are poorer than when fish have undergone death freezing. This has been one of the main barriers to the production of lightly salted products in the same way as in the case of wild fish. Therefore, it was decided to better investigate the effect of salting methods and the composition of brine on the utilization, quality and chemical content of products, in the project "New processes in the processing of farmed cod" (R 11 006-010). Experiments were made with different composition of brine, salt concentration, as well as the use of phosphates and a mixture of citrate and ascorbate. The substances can affect the waterproofing properties of the muscle, partly due to the effect on ionic strength but also due to the specific activity of the substances:
- Citrate binds divalent ions such as calcium (Ca2+) and magnesium (Mg2+) and thus has a positive effect on water resistance. The substance is thought to inhibit the breakdown of glycogen (energy reserves) to some extent, but at the same time, evidence has also been found that it accelerates muscle gain. The substance alone can lower the muscle acidity, which is negative in terms of water resistance, but is offset by the inhibitory effect of the substance on the decrease in acidity due to death stiffness.
- Phosphate can have a positive effect on acidity, bind divalent ions and reduce the cross-linking between actin and myosin. Therefore, the contraction of the muscle may be less.
- Salt (NaCl) can increase muscle contraction with death stiffness, but release decreases and less force is needed to remove pin-bones. Salt has a positive effect on water resistance as salt ions bind to muscle proteins and increase the repulsive force between them. This reduces the risk of water loss from the muscle and it can even increase its weight.
The project showed that great results can be achieved in terms of salt uptake and utilization by controlling the salting technique and brine concentration. The results indicated that the use of phosphate and a combination of citrate and ascorbate could reduce the development, according to measurements of the development of the subjects. However, these effects were not observed in color measurements or sensory evaluation. Injection results in more micro-organisms spreading across the muscle and therefore the shelf life of thawed fillets is shorter than in the case of untreated fillets. When injection was followed by pre-freezing brine, the efficacy symptoms of lightly salted fillets became stronger after 3-6 months in frost. With longer storage or up to 9 months, the difference decreased compared to fillets that were only injected before freezing. In general, symptoms such as cravings, odor of cold storage and taste of cold storage became more pronounced over time, regardless of the salting methods or the composition of the brine.
The project was a joint project of Hraðfrystihús - Gunnvarar hf in Súðavík and Matís ohf in Reykjavík. The AVS Research Fund financially supported the project. AVS reference number: R 006-10
For further information Kristín Anna Þórarinsdóttir at Matís.